This invention relates to an improved transmission lilne device for delaying electromagnetic energy and a method of manufacturing such a device.
Hollow metallic tubes (waveguides) of various transverse cross-sectional shapes exhibit well-known properties which fit them for use as a delay mechanism for electromagnetic waves. Such tubes, which propagate TE waves, are characterised by a wide bandwidth capability and a low insertion loss which is essentially constant over the operating range.
The family of transmission lines which include suspended stiplines, image line, coaxial line, and so on, propagate TEM or quasi-TEM waves and are also suitable for use as delay lines, but such devices, in general, exhibit a higher insertion loss due, in part, to energy losses in the dielectric component.
The cost of amplification at microwave frequencies is high. Consequently insertion loss will be an important consideration where a design calls for a substantial delay. The use of a waveguide may be indicated by virtue of its characteristic low insertion loss, but where the design is also sensitive to cost, weight and volumetric efficiency, the deployment of many metres of commercial waveguide section is likely to pose a problem.
According to our earlier invention, as published under PCT No. AU85/00171, an improved waveguide delay line is disclosed comprising a helical conducting channel formed in a cylinder, such as by machining, such channel being closed by a tightly-fitting conducting sleeve.
The method there disclosed, of fabricating a waveguide delay line for use at microwave frequencies, teaches a way of retaining the low insertion loss characteristic of a waveguide, whilst affording improved volumetric efficiency, low weight and low cost of manufacture. In addition, a delay line so constructed can be integrated into a parent structure as a load-bearing member.
It will be appreciated that in many weight-sensitive applications this duality of electronic function and mechanical load-bearing capability enhances the cost-effectiveness of the method of fabrication disclosed.
In summary, a waveguide delay line as described in the earlier Patent specification confers certain advantages:
(a) a structure that can be integrated into a system as a load-bearing member occupying minimum volume; PA1 (b) extremely low weight per unit delay; PA1 (c) low cost of manufacture; PA1 (d) low cost penalty for varying design parameters; PA1 (e) the low insertion loss characteristic of a normal commercial waveguide.